The attacker, who jumped a wall to get inside, also wounded four other children at the private preschool, known as the Good Shepherd Center, in the city of Blumenau, said police and government officials in the state of Santa Catarina.

He then rode a motorcycle to a state police station and handed himself in, police said.

Dozens of people gathered outside the preschool, whose external wall is covered in bright paintings of children and butterflies. Emergency workers and police had set up a security cordon, and were only allowing parents inside.

One parent outside was Bruno Bridi, the grief-stricken father of five-year-old Bernardo, who was killed. He told journalists how Bernardo and a friend had been hopping like bunnies when he dropped him off at school in the morning.

"I just thank God for every moment I spent with my son," he said through tears.

Brazilian media carried images of small bodies covered in white sheets on the preschool's playground, and a sobbing mother leaving the building carrying her son, who survived the ordeal.

Andre Nazario, whose wife works at the school, said she had described a horrific scene when he spoke with her.

"She said that after the guy left, she went to the playground and saw the (victims). She tried to do CPR on one of them, apparently, but it didn't work. She was in a state of shock," he told journalists.

The attacker mainly struck his victims in the head, emergency official Diogo de Souza Clarindo told journalists.

He killed three boys and one girl, who were between five and seven years old, Clarindo said.

The wounded children -- two girls, both aged five, and two boys, ages three and five -- were in stable condition, said the hospital treating them.

- 'He went to kill' -

Authorities said the attacker was a Santa Catarina resident with at least four prior arrests, including for stabbing his step-father.

He acted alone, police chief Ulisses Gabriel told a news conference, ruling out a "coordinated" attack.

A teacher at the preschool, Simone Aparecida Camargo, described hiding several children in a bathroom as the attacker killed his victims on the playground.

"He went to the playground to kill," she told news site Metropoles.

Blumenau, a normally quiet city of 360,000 people, canceled school and Easter Sunday celebrations, declaring 30 days of mourning.

President Luiz Inacio Lula da Silva condemned the attack.

"There is no greater pain than a family that loses children or grandchildren, even more so when it is in an act of violence against innocent and defenseless children," he wrote on Twitter.

"My thoughts and prayers are with the victims' families and the community of Blumenau in the face of this monstrous attack."

He later held a minute's silence for "the victims of this barbarity" before an event at the presidential palace.

- Repeat tragedies -

Violent school attacks have been increasing in Brazil in recent years.

Last week, a 13-year-old boy killed a teacher in a knife attack at a school in Sao Paulo.

A 16-year-old shooter last November also killed four people and wounded more than 10 others in twin attacks on two schools in the southeastern city of Aracruz, in Espirito Santo state.

The country's deadliest school shooting left 12 children dead in 2011, when a man opened fire at his former elementary school in the Rio de Janeiro suburb of Realengo, then killed himself.

There have also been a series of cases of deadly violence at preschools.

In 2017, a guard at a preschool in the southeastern town of Janauba doused a group of children and himself in alcohol and set them on fire, killing nine children and a teacher and leaving around 40 wounded.

Authorities said the man, who also died, suffered from "mental problems."

In 2021, an 18-year-old man killed three young children and two employees in a knife attack on a preschool in the town of Saudades, Santa Catarina, the same state where Wednesday's attack occurred.